Leviticus chapter 16 is describing the Day of Atonement, or what Israel calls Yom Kippur (Yom means “day”; kaphar means “to cover”). This is the great day of the Jewish calendar that is celebrated on the tenth day of the seventh month, somewhere between the end of September to the beginning of October. The Day of Atonement was the only day of fasting on the Jewish calendar that originated from the Mosaic Law.  It was the day when the holy sanctuary was cleansed of sin and all the sins of the nation where forgiven (except the sin of blasphemy which is described as “sins defiantly” or an intentional sin in Numbers 15:30.)

On this day the high priest was allowed to enter the holy of holies in the Tabernacle (the inner room of the sanctuary). This is in contrast to other cultures in the Near East at that time that enter their inner rooms daily to feed their gods and care for the images of their deities.

The high priest was to sacrifice a bull for his own sin, but was also to take two goats. One of the goats was sacrificed for a sin offering for the people, but the other goat was released into the wilderness after having been figuratively covered with the sins of the people. This “scapegoat,” (“escape goat,” “goat of departure,” or “Azazel”) was released into the wilderness in order to symbolize the removal of sin and its return back to the source of all sin, chaos, barrenness, death and destruction.

Blood from the bull and the goat were taken into the most holy place and placed on the atonement cover (or, the mercy seat) and sprinkled before the Ark of the Covenant. The sanctuary, including the altar of burnt offering, was sprinkled with the blood of the bull to cleanse it from the sins of the priests and with the blood of the goat to cleanse it from the sins of the people.

When the high priest entered the Holy of Holies he was to have a censer full of hot charcoal taken from the altar of burnt offering to burn incense. The incense would create a smoke which would serve as a screen to cover the mercy seat. It appears that this smoke screen from the incense would protect the priest from seeing the presence of God, but also, from other references, it appears the incense smoke would protect the sinner from being seen by God, or at least, the incense would avert the wrath of God. (Psalm 131:2; Numbers 16:46-50.

"“Having fully realized that the whole world is dissolving before our very eyes, it is impossible to ask a more far-reaching question than this: 'Do you believe in Jesus Christ?' ” 

-Dr. Charles Malik, presided over the thirteenth session of the United Nations General Assembly in 1958

The meticulous Jewish scribes who copied scripture before the invention of the printing press had to follow these guidelines:

1. Parchment made only from skins of clean (not unclean according to the Law) animals.
2. Writing quills from feathers of clan birds.
3. Ink must be black and be prepared to specifications.
4. No word could be written from memory, but must first
be read, pronounced out
loud and then written.
5. Before writing the name of God the scribe would wipe
his pen while saying, "I am writing the name of God for
the holiness of his name."
6. No letter could touch another letter. This would invalidate the scroll.
7. Each column must be exactly like the manuscript being copied with no few
than 48 lines and
no more than 60.
8. Within thirty days of being completed an editor would review the work of the scribe, count every letter, count every word and check the middle word of the original
manuscript with the
middle word of the copy.
9. Three mistakes on any page could be corrected within thirty days. Any more than three mistakes on any single page the manuscript was buried.

The oldest copy of the Hebrew Bible before the discovery of the Dead Sea Scrolls in 1947 was the Masoretic Text that came to us in Codex Leningrad from 1000 AD. In the Dead Sea Scrolls a copy of the book of Isaiah from 100 BC was discovered. When compared to the Codex Leningrad that had been copied 1,100 years later (100 BC to 1000 AD) the text of Isaiah was virtually still word for word after 1,100 years of being copied by the scribes.
(Details here, here and here.
Scribes here and here. )